Super light field lens with focus control and non spherical lenslet arrays

ABSTRACT

Light field imaging systems, and in particular light field lenses that can be mated with a variety of conventional cameras (e.g., digital or photographic/film, image and video/movie cameras) to create light field imaging systems. Light field data collected by these light field imaging systems can then be used to produce 2D images, right eye/left eye 3D images, to refocus foreground images and/or background images together or separately (depth of field adjustments), and to move the camera angle, as well as to render and manipulate images using a computer graphics rendering engine and compositing tools.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/US2011/031136, filed Apr. 4, 2011, entitled “Super Light-Field Lenswith Focus Control and Non-Spherical Lenslet Array.” This application isalso a continuation-in-part of U.S. application Ser. No. 12/717,842,filed Mar. 4, 2010, entitled “Super Light Field Lens,” which claims thebenefit of U.S. Provisional Application Ser. No. 61/252,996, filed Oct.19, 2009, entitled “Super Light Field Lens.”

BACKGROUND

The present invention relates generally to optical systems, and moreparticularly to light field imaging systems or plenoptic imagingsystems.

In prior light field gathering systems, or plenoptic imaging systems, aprime lens typically focuses light onto a lenslet array positioned closeto the focal plane of the prime lens. The lenslet array includes aplurality of microlenses that each refracts light to thereby form aplurality of microlens images that are collected by a sensor locatedproximal the focal plane of the microlenses. Typically this distance tothe sensor is on the order of a couple to a few millimeters (mm) fromthe lenslet array as determined by the aperture and f# of themicrolenses. Hence, prior systems were constrained as they could not beused with cameras which typically require a minimum lens clearance ofabout 30 to 40 mm, which far exceeds the 3 or 4 mm clearance provided bythe lenslet array. Further, adapting cameras to work with such aplenoptic imaging system can be a costly and onerous solution.

Therefore it is desirable to provide systems and lenses that overcomethe above and other problems, including lens systems that mate withcameras.

BRIEF SUMMARY

The present invention provides light field imaging systems, and inparticular light field lenses that can be mated with a variety ofconventional cameras (e.g., digital or photographic/film, image andvideo/movie cameras, and DSLR cameras) to create light field imagingsystems. Light field data collected by these light field imaging systemscan then be used to produce 2-dimensional (2D) images, right eye/lefteye 3D images, to refocus foreground images and/or background imagestogether or separately (depth of field adjustments), and to move thecamera angle, to name a few examples. The data can also be used torender and manipulate images using a computer graphics rendering enginesuch as RenderMan® for example in a post-production process.

In one embodiment, a light field imaging system includes a field lens, alenslet array positioned proximal the focal plane of the field lens anda relay optical element configured to gather the light field refractedby the lenslet array, to collimate the light field and to focus thelight field onto an image plane. A sensor, such as a CCD sensor, a CMOSsensor or photographic film may be located proximal the image plane tocapture resulting images.

In one embodiment, a super plenoptic lens is provided that includes afield lens and a lenslet array positioned proximal the focal plane ofthe field lens. The lens also includes relay optical elements configuredand arranged to collimate and focus light refracted by the lenslet arrayonto an image plane. A sensor, such as a CCD sensor, a CMOS sensor orphotographic film may be located proximal the image plane to captureresulting images.

In certain aspects, a field lens can be used with a prime lens (or anyother fixed focal length lens) or a zoom lens. Also, any prime lenseswith a large numerical aperture may be used, such as master primelenses.

In one embodiment, each element of the plenoptic imaging system isinterchangeable during use. For example, the lenslet array (e.g., alenslet array element) may be interchanged, the prime lens may beinterchanged, and the camera or sensor system itself may be interchangedto facilitate adaptability during use. Software stored in a controllersystem can include preset information, calibration information, etc. foruse in controlling the plenoptic camera depending on the particularcharacteristics of the components being used.

In one embodiment, a method of calibrating a superplenoptic lens havinga lenslet array is provided. The method typically includes obtaining afield of images including a plurality of images, each lenslet imagecorresponding to a lenslet in the lenslet array, filtering the field ofimages, identifying a plurality of extrema in the filtered images, andusing the extrema to determine locations and spacings of the lensletimages. The extrema may be maxima, e.g., peaks, or minima. In certainaspects, filtering the field image includes performing anautocorrelation.

According to another embodiment, a method is provided for processing animage acquired using a plenoptic camera having a lenslet array elementcomprising a plurality of lenslets arranged in an array, the lensletarray element being positioned to refract light from a field lens to arelay lens, the relay lens being positioned and configured to gatherlight refracted from the lenslet array and to focus the gathered lighton to a sensor element. The method typically includes acquiring an imageof a light field using the sensor element, the acquired image includingan array or matrix of individual lenslet images, determining depthinformation for the light field using the acquired image, and adjustingthe image using the depth information for the light field to produce anadjusted image. The adjusted image may represent a new camera (e.g.,different angle or position of the camera), or it may include differentfeatures in focus, or it may include a 2-D or a 3-D representation. Incertain aspects, adjusting includes adjusting the focus of features ofthe image such that different image planes in a scene are in focus. Incertain aspects, adjusting includes changing one of a camera angle orcamera position with respect to one or more objects in the acquiredimage using a post-acquisition process. In certain aspects, adjustingincludes one of moving the camera position forward or backwards, panningthe camera, tilting the camera or zooming the camera. In certainaspects, the method is executed for a series of images, e.g., for motionpicture processing.

Various embodiments described herein advantageously allow for the lensto gather the light field rather than a camera or sensor. Lensesaccording to various embodiments can be configured with appropriateoptical manipulation characteristics and physical dimensions to allowfor coupling with a variety of cameras.

In certain aspects, the system has a small form factor to facilitateportable use. For example, the system could attach to the back of acamera rig and the camera and data system could both rest on anoperator's shoulder. The data system in certain aspects is configured tooperate using internal battery power, but could also operate using aconnection to an external power source.

According to one embodiment, a system for plenoptic photography isprovided. The system typically includes a lenslet array elementincluding a plurality of non-spherical-shaped lenslets arranged in anarray, and a sensor element. The system also typically includes anoptical relay element positioned between the lenslet array element andthe sensor element, the relay element being configured to gather lightrefracted from the lenslet array and to focus the gathered light on tothe sensor element. In certain aspects, the non-spherical-shapedlenslets include polygonal-shaped lenslets. In certain aspects, thenon-spherical-shaped lenslets include hexagonal-shaped lenslets.

According to another embodiment, a lenslet array element is providedthat typically includes an optical flat, and a plurality of lensletfeatures etched on the optical flat, the plurality of lenslet featuresincludes a plurality of non-spherical-shaped lenslets arranged in anarray. In certain aspects, the non-spherical-shaped lenslets includepolygonal-shaped lenslets. In certain aspects, the non-spherical-shapedlenslets include hexagonal-shaped lenslets.

According to yet another embodiment, a lenslet array element is providedthat typically includes an optical flat, a plurality of lenslet featuresarranged on the optical flat, and a fiducial mark feature on the opticalflat, e.g., that allows or facilitates alignment of the lenslet arrayelement in an optical system. The mark may include a flat edge orflattened portion of the optical flat.

According to another embodiment, a plenoptic camera is provided thattypically includes a prime lens having a focal plane, a first focusingelement coupled with the prime lens and configured to adjust a positionof the prime lens along an optical axis, and a lenslet array elementpositioned proximal to the focal plane. The camera also typicallyincludes a second focusing element coupled with the lenslet arrayelement and configured to adjust a position of the lenslet array elementalong the optical axis, a relay element configured to collimate lightrefracted by the lenslet array and to focus the light onto an imageplane, and a sensor positioned at the image plane.

According to still a further embodiment, a plenoptic camera is providedthat typically includes a prime lens having a focal plane, a lensletarray element positioned proximal to the focal plane, and a relayelement, including a field lens, and configured to collimate lightrefracted by the lenslet array and to focus the light onto an imageplane. The camera also typically includes a sensor positioned at theimage plane, and at least a first focusing element coupled with one ofthe prime lens or the lenslet array or the field lens, and configured toadjust a position of the prime lens or the lenslet array or the fieldlens along an optical axis. In certain aspects, the camera furtherincludes a second focusing element coupled with and configured to adjustone of the other of the prime lens or the lenslet array or the fieldlens along an optical axis.

Reference to the remaining portions of the specification, including thedrawings and claims, will realize other features and advantages of thepresent invention. Further features and advantages of the presentinvention, as well as the structure and operation of various embodimentsof the present invention, are described in detail below with respect tothe accompanying drawings. In the drawings, like reference numbersindicate identical or functionally similar elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIGS. 1A and 1B illustrate a relay element according to one embodiment.

FIGS. 2A and 2B are views of a more detailed example of a housingstructure according to one embodiment; FIG. 2A shows a sidecross-section view, while FIG. 2B shows a side view, end view, andperspective view.

FIG. 3 is an example of optical elements for a specific light fieldimaging system according to one embodiment.

FIG. 4 is a block diagram of a computer system that may be used topractice embodiments of the present invention.

FIGS. 5A and 5B illustrate two pictures of a lens according to oneembodiment; FIG. 5A shows a lens coupled with a film camera and FIG. 5Bshows a lens coupled with a digital camera.

FIGS. 6 and 7 illustrate examples of relay lenses having specificarrangements of optical elements according to certain embodiments.

FIG. 8 shows a Polychromatic Diffraction MTF (Modulation TransferFunction) for a super plenoptic lens.

FIG. 9 illustrates a spot diagram for a super plenoptic lens.

FIG. 10 illustrates a graph of Lens f# vs. Lenslet f# vs. f-stops of aPrime lens.

FIG. 11 illustrates a graph of lenslets vs. image circle diameter forvarious light field cameras.

FIG. 12 illustrates image circle metadata for a superplenoptic lens asshown in FIG. 7.

FIGS. 13A-13C show lenslet vs. image circle metadata for the lens ofFIG. 7.

FIG. 14 shows data for various motion picture prime lenses.

FIG. 15 shows a method of calibrating images according to oneembodiment.

FIG. 16 shows an example of an autocorrelation image showing peaks orextrema.

FIG. 17 shows an example of a histogram for the inter-peak distances.

FIG. 18 illustrates an example of a lightfield image captured using aplenoptic lens.

FIG. 19 illustrates elements of a focus controller system according toone embodiment.

FIG. 20 illustrates an example of a lenslet array element (shown as anoptical flat with no visual detail shown of the lenslets, which can becircular, non-circular, e.g., hexagonal, etc.) according to one specificembodiment.

FIG. 21 illustrates an example of hexagonal-shaped lenslet packingaccording to one embodiment.

DETAILED DESCRIPTION

FIGS. 1A and 1B illustrate a relay element according to one embodiment.As shown in FIG. 1A, a first set of optical elements in the front tube(including a field lens such as a prime lens) receives light refractedby the lenslet array (not shown) and collimates and focuses that lightonto a second set of optical elements in the rear tube, which focus thelight onto an image plane (not shown). A sensor, e.g., CCD, CMOS orfilm, positioned at the image plane receives and records image(s). FIG.1B shows a perspective view of an example of a housing structure (e.g.,lens barrel), with the relay lens on the left side.

In certain aspects, the field lens, lenslet array and relay opticalelements are contained within a housing structure (e.g., lens barrel)that allows for adaption of distance between the various elements, e.g.,by manual rotation or manipulation, or by electronic control via acontroller subsystem. FIGS. 2A and 2B are views of a more detailedexample of a housing structure (e.g., lens barrel), including elements(e.g., threads, bearings) to allow for manipulation and adjustment ofspacings of optical elements according to one embodiment; FIG. 2A showsa side cross-section view; FIG. 2B shows a side view, end view, andperspective view. In certain aspects, the various optical elements arecontained within a housing structure at fixed distances.

FIG. 3 is an example of optical elements for a specific light fieldimaging system according to one embodiment. It should be understood thatthe dimensions and specific elements may be changed as would be apparentto one skilled in the art based on the teachings herein. Light isfocused by the field lens onto a focus plane (approximately 45 mm-108.5mm from the prime in this example). A field lens can include a primelens (or any other fixed focal length lens) or a zoom lens. A lensletarray positioned proximal the focus plane refracts the light into aplurality of images. The light refracted by the lenslet array iscollected, collimated and focused by the first set of optical elementsonto a second set of optical elements as shown. The second set ofoptical elements is configured and arranged to focus that light onto animage plane as shown. Again, a sensor located proximal the image planecollects image data (e.g., digital data in the case of CCD or CMOSsensors, or latent images in the case of film). In the example shown,the image plane is approximately 240 mm-300 mm from the lensletarray/focal plane of the prime. In certain aspects, with appropriateselection and/or adjustment of elements in the relay lens, the distancebetween the image plane and the lenslet array can be set at, or adjustedto be, from about 30 mm to about 300 mm or greater.

FIGS. 6 and 7 illustrate examples of relay lenses having specificarrangements of optical elements according to certain embodiments.

In certain aspects, it is desirable that the f# of the prime match thef# of the lenslet array to allow for better image separation at thelenslet array. In certain aspects, the f# of the prime should be thesame as or less than the f# of the lenslet array. For example, a primehaving f/2.8 or f/4 would work well with a lenslet array having f/2.8,or f/4, respectively.

In certain aspects, it is desirable to take the output of the lightfield image system and process the image data, e.g., to convert it todifferent formats for post processing functions such as depth mapformats for compositing, manipulating and rendering 2D images, toproduce right eye/left eye 3D images, to refocus foreground imagesand/or background images together or separately (depth of fieldadjustment), and to move the camera angle, etc. According to oneembodiment, a process for such a pipeline begins with camera dataacquisition (e.g., acquire raw image files), then camera calibration(e.g., process and store calibrated light fields) and then light fieldrendering (e.g., to produce DPX, TIFF, EXR or zmap files or other filetypes). For digital sensors, an interface with a storage subsystem orcomputer system allows for data transfer. For film, scanning of imagesusing a film scanner can be performed to produce digital data.

FIG. 4 is a block diagram of a computer system that may be used topractice embodiments of the present invention, in particular image datacalibration (see below), data processing and image manipulation andrendering. FIG. 4 is merely illustrative of an embodiment incorporatingthe present invention and does not limit the scope of the invention asrecited in the claims. One of ordinary skill in the art would recognizeother variations, modifications, and alternatives.

In one embodiment, computer system 400 typically includes a 2D or 3Dmonitor 410, computer 420, a keyboard 430, a user input device 440,computer interfaces 450, and the like.

In various embodiments, user input device 440 is typically embodied as acomputer mouse, a trackball, a track pad, a joystick, wireless remote,drawing tablet, voice command system, eye tracking system, and the like.User input device 440 typically allows a user to select objects, icons,text and the like that appear on the monitor 410 via a command such as aclick of a button or the like.

Embodiments of computer interfaces 450 typically include an Ethernetcard, a modem (telephone, satellite, cable, ISDN), (asynchronous)digital subscriber line (DSL) unit, FireWire interface, USB interface,and the like. For example, computer interfaces 450 may be coupled to acomputer network, to a FireWire bus, or the like. In other embodiments,computer interfaces 450 may be physically integrated on the motherboardof computer 420, and may be a software program, such as soft DSL, or thelike.

In various embodiments, computer 420 typically includes familiarcomputer components such as a processor 460, and memory storage devices,such as a random access memory (RAM) 470, disk drives 480, a GPU 485,and system bus 490 interconnecting the above components.

In some embodiments, computer 420 includes one or more Xeonmicroprocessors from Intel. Further, in one embodiment, computer 420includes a UNIX-based operating system.

RAM 470 and disk drive 480 are examples of tangible media configured tostore data such as image files, models including geometricaldescriptions of objects, ordered geometric descriptions of objects,procedural descriptions of models, scene descriptor files, shader code,a rendering engine, embodiments of the present invention, includingexecutable computer code, human readable code, or the like. Other typesof useful tangible media include floppy disks, removable hard disks,optical storage media such as CD-ROMS, DVDs and bar codes, semiconductormemories such as flash memories, read-only-memories (ROMS),battery-backed volatile memories, networked storage devices, and thelike.

In various embodiments, computer system 400 may also include softwarethat enables communications over a network such as the HTTP, TCP/IP,RTP/RTSP protocols, and the like. In alternative embodiments of thepresent invention, other communications software and transfer protocolsmay also be used, for example IPX, UDP or the like.

In some embodiments of the present invention, GPU 485 may be anyconventional graphics processing unit that may be user programmable.Such GPUs are available from NVIDIA, ATI, and other vendors. In thisexample, GPU 485 includes a graphics processor 493, a number of memoriesand/or registers 495, and a number of frame buffers 497.

FIG. 4 is representative of a computer system capable of embodying thepresent invention. It will be readily apparent to one of ordinary skillin the art that many other hardware and software configurations aresuitable for use with the present invention. For example, the computermay be a desktop, portable, rack-mounted or tablet configuration.Additionally, the computer may be a series of networked computers.Further, the use of other microprocessors are contemplated, such asPentium™ or Itanium™ microprocessors; Opteron™ or AthlonXP™microprocessors from Advanced Micro Devices, Inc; and the like. Further,other types of operating systems are contemplated, such as Windows®,WindowsXP®, WindowsNT®, or the like from Microsoft Corporation, Solarisfrom Sun Microsystems, LINUX, UNIX, and the like. In still otherembodiments, the techniques described above may be implemented upon achip or an auxiliary processing board.

FIGS. 5A and 5B illustrate two pictures of a lens according to oneembodiment; FIG. 5A shows a lens coupled with a film camera and FIG. 5Bshows a lens coupled with a digital camera.

Lenslet Array Elements

In certain embodiments discussed above, the lenslet array includes aplurality of circular shaped lenslets arranged in an array. In anotherembodiment, a lenslet array, or a lenslet array element, includes aplurality of polygonal shaped lenlets arranged in an array. Withspherical shaped lenslets, even for a densely packed array,approximately 24% of the image may be lost due to the packingconstraints of spherical shaped features. Polygonal shaped elements canadvantageously be more densely packed so that less image is lost due togreater coverage of the area of the lenslet array element by theindividual lenslets. FIG. 21 illustrates an example of hexagonal-shapedlenslet packing according to one embodiment. For example, with hexagonalshaped lens-let packing (for use in a plenoptic lens) the loss may bereduced to about 10 to 12%, advantageously providing a substantial gainin resolution. In general, hexagonal features provide for the densestpacking in a plane and minimize wastage. In certain aspects, a packingdensity of between about 100 lenslets per (linear) inch and about 300per inch or more can be used. Other polygonal and non-spherical shapesor geometries may be used. Additionally, differently shapes/geometriesof lenslets may be used, and/or different sizes of lenslets may be usedto form the array of lenslets.

In another embodiment, a doublet lenslet array element is provided(compared to a single lenslet array element discussed above). In thisembodiment, two lenslet array elements are glued or otherwise bondedtogether to form a doublet lenslet array element. Each individuallenslet array element includes a plurality of lenslets arranged in anarray. In this embodiment, light from the field lens interacts with(e.g., is refracted by) the first lenslet array, and then interacts withthe second lenslet array. Such an arrangement advantageously allows forreduced diameter of the optical components of the relay lens, forexample. With a single lenslet array, for example, diffraction at theedges may provide a 35 degree angle (growing, away from optical axis),whereas with the doublet arrangement, diffraction at the edges of thedoublet provides a decreased angle, for example 20 degrees, therebyproviding a reduced diameter light field. This in turn allows for asmaller barrel housing size. It is important that each lenslet in thedoublet includes a different material. For example, in certain aspects,one lenslet array element of the double can be a positive lens and theother lenslet array element can be a negative lens, with thecombination/doublet forming a positive lens. Chromatic aberration isadvantageously be reduced with a doublet arrangement, and the refractionangle is advantageously reduced as well as the barrel size needed. Anyof a variety of optical materials/glasses may be used as desired for theappropriate design specifications, e.g., f#, packing density, etc.Examples of useful optical materials include fused silica, borosilicate,fused quartz, etc. In general any pairing of crown and flint glass maybe used.

Calibration

A superplenoptic lens, such as disclosed herein, makes images using alenslet array. Each image is a rectangular array of sub-images, one perlenslet. Pixels in the lenslets are indexed by 4-dimensionalcoordinates—2 dimensions to select a sub-image and 2 further coordinatesto select pixels from the sub-images. In one embodiment, the pixelcoordinates are taken to range from −½ to ½ across each sub-image, sothe nominal size of the sub-image is 1×1, with its center at coordinate(0,0). Because the sub-images are indexed with integers, the 4coordinates can be reduced down to 2 numbers by addition, so the integerparts of the 2-dimensional coordinates identifies the sub-image and thefractional parts (e.g., between −0.5 and 0.5) select pixels withinsub-images.

To use images captured by a superplenoptic lens, it is necessary to mapcoordinates in lenslet space to coordinates in the image. The mappingcan be approximated well with an affine transformation, possiblycombined with a radial distortion term. The calibration processapproximates the lenslet-to-sensor mapping, starting with a framecaptured by the superplenoptic camera. No special calibration target isrequired, any well-lit frame will do. The calibration procedure relieson the fact that due to vignetting by the lenslets, the sub-images aremostly bright in the middle and black near the corners.

In certain embodiments, an autocorrelation of the calibration image isfirst calculated. This value will be large at positions corresponding tomultiples of the lenslet spacing (and at other points, due to noise).Peaks are extracted from the autocorrelation and a histogram of pairwisedistances between the peaks is made. The first local maximum of thehistogram (above a certain noise threshold) gives an estimate of thelenslet spacing. It should be appreciated that minima could also beused. Second, the estimated spacing is used as the filter width of alow-pass filter that is run over the original image. This blurs out alldetails within the lenslets, leaving (mostly) only bright spots centeredon the lenslet centers. Another peak-detection pass selects candidatelenslet centers from the filtered image.

Next, the candidate list is culled; for each candidate, the number ofneighboring points within a certain percentage (e.g., 20%) of theoriginal lenslet spacing estimate is counted. If there are exactly 4such neighbors, the candidate point is accepted. By walking the neighborgraph of the accepted points, a lenslet number is assigned to each.Finally, a least-squares fit of the lenslet-to-sensor mapping fitting isapplied to the assigned lenslet numbers and measured locations of eachacceptable candidate.

As discussed above, in order to use the images taken using a plenopticlens according to the embodiments described herein, it is desirable tocalibrate the images to determine the locations and dimensions of thelenslet images within each image. According to one embodiment, a method1500 of calibrating images is shown in FIG. 15. In step 1510, an imageis acquired. The image acquired (e.g., lenslet image) includes an arrayor matrix of individual lenslet images. FIG. 18 illustrates an exampleof a lightfield image captured using a plenoptic lens. As can be seen,the lightfield image includes a plurality of tiny images taken fromdifferent viewpoints.

Certain features of the image are sufficiently unknown that it isdifficult to know the dimensions of each lenslet image. For example, theangle of the lenslet array relative to the image plane (sensor) is notknown and the magnification of the relay lens is not sufficiently known.Even with robust components, the image plane angle may vary from shot toshot due to movement of the camera, for example, as the camera andcomponents are not sufficiently rigid. For example, over a range of 20pixel images, movement might be on the order of 0.5 pixels, whereas a0.1 pixel or better resolution is generally needed. Also, the lensletarray may be canted relative to the image plane; the angular deviationof the lenslet array to the sensor array is typically on the order of0.5 degrees or less. Therefore, the dimensions of the lenslet images arenot sufficiently known.

In step 1530, an optional autocorrelation function is applied toauto-correlate the lenslet images to determine spacing parameters of thelenslet images. Generally, the autocorrelation function involvesconvolving the lenslet array image with itself; the image is correlatedwith itself at different offsets and it becomes desirable to identifythe offset that lines up identical features in the various lensletimages. In certain embodiments, an a priori estimate of the lensletspacing could be used in place of autocorrelation. In general,autocorrelation is used to determine what filter to use when filteringthe field image to enhance the peaks. Hence, in one embodiment, a stepof identifying a peak enhancement filter is performed before a step offiltering the field image, where autocorrelation is one way used toidentify a peak enhancement filter.

In one embodiment, an optional blur filter is applied to the lensletimages at step 1520 before auto-correlation. This is done to removedetail from the images as detail in the images is not important fordetermining spacings, dimensions and locations of the lenslet images.Generally any blur filter may be used as no parameters need to be tuned.

The result of the autocorrelation step 1530 produces an image ofregularly spaced spikes or peaks representing all possible offsets. Anexample of the autocorrelation image showing peaks is shown in FIG. 16.In step 1540, a histogram of inter-peak distances is created for allpossible pairs of peaks (or a subset of all pairs of peaks). Forexample, a list of x and y coordinates for the peaks is created, and foreach peak, a list of distances between all other peaks is determined.FIG. 16 shows distances for the three closest peaks to peak 1601. Ahistogram of inter-peak distances is then formed. An example of such ahistogram is shown in FIG. 17. As can be seen, a series of histogrampeaks results. Generally, the first histogram peak represents a goodestimate of the lenslet size (e.g., the spacing between peaks representsa good estimate for the vertical and horizontal dimension of eachlenslet image in the array). In general, there may be some noise, due tofor example peaks such as peak 1603, in this case the inter-peakdistance between peak 1602 and 1603 creates a noise count. If desired,in one embodiment, noise can be reduce by removing a portion of thedata, for example removing all histogram peaks below a threshold valuefrom the data. In certain aspects, the threshold value is set at apercentage (e.g., 5, 10 or 15 percent of the max histogram peak height).

In step 1550, directions of the lenslet images are determined. As above,the lenslet images may be canted relative to the image plane, e.g., byabout 0.5 degrees or so. In one embodiment, the directions of vectorsrepresenting the closest peaks along x and y directions (based on thex-y coordinates of peaks) are sorted into two buckets, or bins, andaverages are taken of each bucket to determine average perpendicularinter-peak directions. Because the cant is typically less than 0.5degrees, one bucket will generally consist of vectors having apredominant x component, and the other will consist of vectors having apredominant y component. Hence the average of each bucket provides anestimate of the directions between lenslet images.

In step 1560, the center positions of the lenslet images are determined.In one embodiment, this is done by first assuming that the corner is atthe origin. All images are then added up, which typically results in ablack spot oriented in the center of the composite image. The positionof this spot relative to the corner can be used to determine the offsetto determine the position of the corner of a lenslet image. Each centerspot should have exactly 4 neighbors at correct distances in a matrix;lenslet coordinates can be assigned to each center (e.g., with anarbitrary coordinate assignment for the matrix origin) and a leastsquares fit can be used to obtain the calibration matrix.

It should be appreciated that the calibration methodologies describedherein may be performed offline after image capture, or they may beperformed in real time as images are being captured.

Calibration Function

One embodiment of a calibration function includes a simple affinetransformation. That is, it is assumed that there is a linearrelationship between lenslet coordinates and pixel coordinates. Thereare six parameters, (e.g., a, b, c, d, e, and f) such that if (x,y) is apoint in lenslet space and (X,Y) is a point in pixel coordinates, then:

X=ax+by +c

Y=dx+ey+f

The least-squares optimization to find a, b, c, d, e, and f works asfollows:Given a bunch of pairs of corresponding points

((X[i],Y[i]),(x[i],y[i])),0<=i<n

(those are the output of the first few phases of the calibrationprocedure), the total squared calibration error for the pairs is:

double error=0; for(i=0;i<N;i++){  double dx=a*x[i]+b*y[i]+c−X[i]; double dy=d*x[i]+e*y[i]+f−Y[i];  error+=dx*dx+dy*dy; }

The optimization process calculates (a, b, c, d, e, and f) to minimizethis error term. In certain aspects, Newton's method is used to find azero of the gradient of the error. The same method works for anycalibration function that is suitably continuous in its parameters.

In some cases, it may be desirable to correct for radial distortion ofthe relay lens as well. In this case, the calibration function can bemade slightly more complex and a few more parameters can be added to beoptimized. For example, in addition to the affine parameters (a, b, c,d, e, and f), there could be three more parameters (g, h, and j) thatspecify the center of the radial distortion and its intensity:

u=ax+by +c−g

v=dx+ey+f−h

r=1+j(u ² +v ²)

X=ur+g

Y=vr+h

The affine part characterizes the shape and orientation of the lensletarray. The distortion part characterizes the relay lens. One can makemore complicated radial distortion models by adding terms with highereven powers of u²+v² (and corresponding extra parameters). In certainembodiments, j substantially equal to 0 and g and h are irrelevant,since they cancel out when j=0.

Collimated Pinholes

In certain aspects, it is desirable to be able to calibrate the camerausing the scene footage the camera crew shot as discussed above. Incertain circumstances where that may be infeasible a flat white fieldcan be used. In this case, the lenslets produce vignetted images of thefield from which lenslet corners and centers can be easily located asdiscussed above. In another embodiment, a calibration image that puts atiny spot at the center of each lenslet is used. To accomplish this, inone embodiment, the field lens is replaced with an illuminated pinholeat the focal plane of a collimating lens. In this case, the order of theelements in the assembly would be

Light source

Pinhole

Collimator

Lenslet array

Relay lens

Sensor

The effect is to project the image of the pinhole out to infinity. Thisconfiguration sends a bundle of parallel rays to the lenslet array,which will focus the rays at the lenslet centers (if the pinhole iscarefully centered to start with.) Then, the lenslet centers can belocated to sub-pixel precision by computing the centroids of theprojected pinhole images. Either target choice (flat field or collimatedpinhole) allows for a list of candidate lenslet locations to beobtained, which can be used to drive the rest of the calibrationprocess.

Depth Estimation

After acquisition of raw frames from the plenoptic camera, the imagesare processed to densely recover depth in the original scene. For thesake of this description, consider that each lenslet image consists of asquare n×n matrix of pixel values. If a corresponding pixel is extractedfrom each of the lenslet images and they are arranged as an image, n×nimages of the original scene can be produced, each imaged from aparticular different position on the main field lens. Because theseimages are obtained from a precision, calibrated screen of preciselydetermined dimension, the relative world space shifts in viewpointbetween all these virtual images are known. This reduces thedimensionality of the search needed to be performed relative to otherless constrained multiple view stereo algorithms. Instead of recoveringindividual camera positions for each of the n×n cameras, one can solvefor their median position.

After recovering the camera position, depth can be determined bydirectly measuring the disparity of each pixel in the image, and fromthe disparity and the world space coordinate information, the relativedepth of each pixel can be determined. Super-resolution techniques arethen used to combine all of the images back together along with depthinformation, and generate a layered depth image which can be used bymore conventional compositing tools that implement depth-basedcompositing.

Image Processing

According to certain embodiments, using the image information obtainedfrom the plenoptic camera, various computational processes can beapplied to the image information to modify and produce images withvaried characteristics. Examples include producing 2D or 3D images,depth of focus changes for still images as well as for motion pictures(series of images), adjusting focus points in images, changing cameraangles or creating new camera views, selectively focusing on near fieldor far field separately or simultaneously. It should be appreciated thatthe image processing methodologies described herein may be performedoffline after image capture, or they may be performed in real time asimages are being captured.

Depth of Focus changes can be applied for motion pictures as well as tostill shots. In this case, a shot in live action can have thefore/middle and/or far ground in focus simultaneously. See, e.g., LightField Photography with a Hand-held Plenoptic Camera by Ren Ng, MarcLevoy, Mathieu Bredif, Gene Duval, Mark Horowitz, Pat Hanrahan, Siggraph2005; and The Light Field Camera: Extended Depth of Field, Aliasing andSuper-resolution by Tom E. Bishop and Paolo Favaro, IEEE TRANSACTIONS ONPATTERN RECOGNITION AND MACHINE INTELLIGENCE, each of which isincorporated by reference in its entirety, for techniques for producingdepth of focus changes.

In one embodiment, extracting depth information from light fieldsinvolves extracting depth information from the lenslet images inmulti-view stereo. For example, with multitudes of lenslet images, e.g.,approximately 20,000 to 25,000 lenslet images, in a typical scene,multi-view stereo can be done either directly on lenslet images or lowresolution images can be constructed by taking corresponding points fromdifferent lenslets. With prior 3D systems, for example, the suddenchanges in the depth of foreground focus in the image caused eye musclesto fatigue quickly. With the present embodiment, by matching the depthof the attention points in the image in the scenes across cuts it (eyefatigue) will be prevented and one is able to adjust depth inpost-production.

In one embodiment, various camera angle computational changes are madein post-production. When the camera is set up in a particular way, onecan slightly change the angle and position of the camera inpost-production using the information provided by the plenoptic camera.In certain aspects, a new camera can be synthesized from the image data.Additionally, a synthesized camera, given the part of the light fieldthat the synthetic camera captures, can be adjusted. Examples of cameraview adjustments, or new camera views that can be created, includetrucking (e.g., moving the camera forward and backward), panning,tilting, zooming, etc.

In one embodiment, selective focus of the image field can beaccomplished using the light field information gathered by the plenopticcamera. For example, in the same image, one can focus on near field andfar field, advantageously providing the ability to have everything infocus at all times. The focus curves for the lenslet cameras typicallyhave two depths at which the focus is anomalous. At one depth all depthand resolution information may be lost. The samples inside the lensletare the same at all pixels; it is convenient to have the focus on oneside of that depth either infinity or up close. Focus control is aboutadjusting the camera to get the maximum amount of information out of it,e.g., to keep the low resolution spots in places where you have no scene(image).

FIGS. 8-14 show various performance parameters for superplenoptic lenscomponents. FIG. 8 shows a Polychromatic Diffraction MTF (ModulationTransfer Function) for a super plenoptic lens. FIG. 9 illustrates a spotdiagram for a super plenoptic lens. FIG. 10 illustrates a graph of Lensf# vs. Lenslet f# vs. f-stops of a Prime lens and FIG. 11 illustrates agraph of lenslets vs. image circle diameter for various light fieldcameras. FIG. 12 illustrates image circle metadata for a superplenopticlens as shown in FIG. 7, and FIGS. 13A-13C show lenslet vs. image circlemetadata for the lens of FIG. 7. FIG. 14 shows data for various motionpicture prime lenses.

Focus Controller System

In one embodiment, a focus controller system includes two focus controlelements, one to control the position of the prime lens relative to thelenslet array and another to control the distance of the lenslet arrayrelative to the relay lens elements. For example, the prime can beadjusted for optimal or maximum replication (to capture a light field),e.g., a rate of 4 or 8, or set at infinity, and the lenslet arrayelement can be adjusted to obtain optimal focus within each lenslet.FIG. 19 illustrates elements of a focus controller system according toone embodiment. As shown, a first focus controller includes a focus ringthat allows for adjustment of the position of the lenslet array elementalong the optical axis. Activation of the focus ring, either manually orautomatically (with a motor coupled with a drive gear) in response to acontrol signal, causes rotation of the ring, which changes the axialdistance of the lenslet array due to the helical coupling between thering and a fixed feature. For automatic focus control, industry standardfollow focus automation can be used. Similarly, a second focus controlelement or ring (not shown) is provided to concomitantly or separatelycontrol the axial location of the prime. The second ring can be eithermanually or automatically controlled. Additionally, another focuscontrol element can be used for adjusting the focus of the field lens.In general, one or multiple focus controllers can be included to controlfocus of any or all of the field lens, the prime lens and the lensletarray.

In one embodiment, a fiducial mark or edge is provided on a lensletarray element to facilitate alignment of the lenslet array in theimaging system. Such a fiducial mark also advantageously reduces oreliminates the need to correct for misalignment after the fact. FIG. 20illustrates an example of a lenslet array element (shown as an opticalflat with no visual detail shown of the lenslets, which can be circular,non-circular, e.g., hexagonal, etc.) according to one specificembodiment. The fiducial mark or edge at the bottom allows for alignmentverification. It should be noted that FIG. 20 shows a specific lensletarray element with specific parameters, however, it should be apparentthat lenslet array elements with varying parameters can be used.

While the invention has been described by way of example and in terms ofthe specific embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements aswould be apparent to those skilled in the art. Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

What is claimed is:
 1. A system for plenoptic photography, the systemcomprising: a) a lenslet array element including a plurality ofhexagonal shaped lenslets arranged in an array; b) a sensor element; andc) an optical relay element positioned between the lenslet array elementand the sensor element, the relay element being configured to gatherlight refracted from the lenslet array and to focus the gathered lighton to the sensor element.
 2. The system of claim 1 wherein the lensletarray element includes a fiducial mark feature on a surface of theelement to assist with alignment of the lenslet array.
 3. The system ofclaim 1 wherein the optical relay element includes a field lens.
 4. Thesystem of claim 1 wherein the relay optical element includes: a firstset of optical elements; and a second set of optical elements, whereinthe first set of optical elements is configured and arranged tocollimate the gathered light and focus the collimated light onto thesecond set of optical elements, and wherein the second set of opticalelements is configured and arranged to focus the light onto the sensorelement.
 5. The system of claim 1 wherein the sensor element includesone of a CCD sensor or a CMOS sensor or photographic film.
 6. The systemof claim 1 wherein the sensor element includes a camera housing thatholds a sensor.
 7. A plenoptic camera, comprising: a prime lens having afocal plane; a first focusing element coupled with the prime lens andconfigured to adjust a position of the prime lens along an optical axis;a lenslet array element positioned proximal to the focal plane; a secondfocusing element coupled with the lenslet array element and configuredto adjust a position of the lenslet array element along the opticalaxis; a relay element configured to collimate light refracted by thelenslet array and to focus the light onto an image plane; and a sensorpositioned at the image plane.
 8. The camera of claim 7 wherein eachfocusing element is manually adjustable.
 9. The camera of claim 7wherein each focusing element is automatically adjustable responsive toa control signal.
 10. The camera of claim 7 wherein each focusingelement includes a servo motor coupled with a focus that automaticallyadjusts a focus ring in response to a control signal received from acontroller subsystem.
 11. The camera of claim 7 wherein the lensletarray element includes a plurality of hexagonal shaped lenslets.
 12. Alenslet array element, comprising: an optical flat; a plurality oflenslet features etched on the optical flat, the plurality of lensletfeatures includes a plurality of hexagonal shaped lenslets arranged inan array.
 13. The lenslet array element of claim 12 wherein the lensletfeatures include at least one spherical shaped lenslet in addition tothe plurality of hexagonal shaped lenslets.
 14. The lenslet arrayelement of claim 12 further comprising: a fiducial mark feature on theoptical flat.
 15. A plenoptic camera, comprising: a prime lens having afocal plane; a lenslet array element positioned proximal to the focalplane; a relay element, including a field lens, and configured tocollimate light refracted by the lenslet array and to focus the lightonto an image plane; a sensor positioned at the image plane; at least afirst focusing element coupled with one of the prime lens or the lensletarray or the field lens, and configured to adjust a position of theprime lens or the lenslet array or the field lens along an optical axis.16. The camera of claim 15 further including a second focusing elementcoupled with one of the prime lens, or the lenslet array element or thefield lens, and configured to adjust a position of the prime lens, thelenslet array element or the field lens along the optical axis.
 17. Thecamera of claim 15 wherein the lenslet array element includes aplurality of hexagonal shaped lenslets.